1. Field of the Invention
The present invention relates generally to the field of prosthetics, and more particularly to a three prong adapter having a hub with an end having a threaded outer surface and is used to interconnect a socket made for a stump of a residual limb and a prosthetic limb.
2. Description of the Related Art
Sometimes, due to accidents, health problems, birth defects, etc., people 5 need to have a limb 6 amputated. The amputated limb 6 terminates in a stump 7. In general, a socket 10 can be formed for a particular stump 7. Those sockets are well known in the art, and each socket 10 has a central axis 11. An adapter is needed to connect the socket to a prosthetic limb.
Fortunately for people requiring a prosthetic limb, many advancements have been made in the field of prosthetic limbs. Patients now have many choices, including endoskeletal and exoskeletal prosthetic limbs. The present invention relates to endoskeletal prosthetic limbs. That is, limbs comprised of structural components and an optional aesthetic outer shell. Several examples of available prosthetic devices are described below.
U.S. Pat. No. 5,458,657 to Rasmusson shows an endoskeletal prosthesis having an adapter assembly. The adapter assembly has a socket coupler embedded within a stump socket. The socket coupler appears generally cup shaped, and appears to have limited ability to adjust to fit with stumps of various sizes. This socket coupler therefore has an undesirable limited practicality. A socket adapter plate is bolted to a bottom side of the socket coupler. The interface between the socket coupler and socket adapter is flat, and that interface lies generally in a plane that is perpendicular to the socket longitudinal axis. Those bolts must be able to withstand and transfer any shear stress between the socket adapter and the socket coupler in the direction generally perpendicular to the socket longitudinal axis. Yet, those bolts may not be designed to withstand large amounts of shear stress.
U.S. Pat. No. 6,013,105 to Potts shows a prosthesis connector and alignment assembly having a rotational positioning module and sliding adjustment. The base is shown as a plate having an annular wall projecting from the plate with external threads. A locking assembly threads onto the threaded annular wall of the base plate. This design is undesirably complicated. Further, no external threads are shown to mate with a separate prosthetic component. The plate only engages the bottom of the socket, which results in a less than optimum structural connection, as the fasteners that connect the plate to the socket have to withstand any and all shear stress between the socket and the plate.
Three prong adapters in existence, such as the one shown in FIG. 1, solve many of the problems associated with the above-described patents. The three prong adapters in existence are relatively simple in design, and are structurally strong while at the same time light weight. One such three prong adapter is sold by American Prosthetic Components Inc., under model number APC-700L. FIG. 1 is representative of this type of adapter. As shown in FIG. 1, existing three prong adapters 20 have three prongs 21. A hole extends through the three prong adapter 20. The hole 22 has a wall 25 with a partition 26. Threads 27 are on the inside of the wall 25. The threads 27 on the inside of the wall 25 are partitioned in a manner that corresponds to the wall partition 26, such that the threads have respective first ends 28 and second ends 29. A clamp 35 is on the outside of the three prongs adapter. A screw 36 can be turned into the clamp 36 to reduce the size of the partition 26 and reduce the circumferential size of the adapter 20 to tighten down on a component threaded into the adapter.
The adapter prongs 21 are used to connect to the lower sides of the socket. One major advantage of a three prong adapter over a plate with a flat interface is that the prongs 21 provide an improved structural connection to a socket compared to a plate, especially in directions perpendicular to a central axis 11 of the socket 10, such as the in lateral and medial directions 15 and 16, respectively, as well as in the anterior and posterior directions 17 and 18, respectively. In this regard, the bolts or laminate do not have to withstand the shear stress in directions perpendicular to the central axis 11 of the socket 10.
A further advantage of the now existing three prong adapters 20 over the other adapters described above is that one or more of the prongs 21 can be bent so that the three prong adapter 20 can better fit with a given socket.
The existing three prong adapters 20 perform well in some circumstances. Yet, even the existing three prong adapters 20 can be improved upon. The wall 25 is completely partitioned to allow the clamp 35 to be able to selectively reduce the size of the hole after an object is threaded into it. This is done in order to clamp down on an object threaded into the adapter 20. However, when one or more prongs 21 are manipulated, or bent, to enable the three prong adapter 20 to better fit on the socket, the threads 27 can become misaligned along the partition 26. When this happens, it can be difficult or impossible to thread an object into the three prong adapter 20.
A further undesirable complication of using the existing three prong adapters is that the laminate used to connect the three prong adapter 20 to a socket 10, which is well known in the art, can sometimes flow into contact with and bond to the threads 27. When this occurs, a prosthetic component may not properly thread into the three prong adapter 20. It is difficult and sometimes impossible to satisfactorily remove laminate that is bonded to the threads 27.
Thus, there exists a need for a three prong adapter that maintains the advantages of the existing three prong adapters, but that also solves these and other problems associated with existing three prong adapters.